Probably something revolutionary... something we couldn't even dream of today. It could include concepts like true multitasking... file transfer from device to device without any special software... freedom to install any kind of application, maybe even write your own, in any language you choose... Maybe - unlikely, but maybe - it would even include a futuristic concept one could name "copy&paste"? Who knows?

I know this sounds incredible in 2011 when not even the iPhone or this brand new WP7 can do most of it, but hey! We're talking about the future! The real future future!